1. Field of the Invention
The present invention generally relates to a call-admission controller and a method of call-admission control, and particularly relates to a call-admission controller and a method of call-admission control in a communications system wherein resources are shared by calls of multiple priority classes.
2. Description of the Related Art
In a public communications system in which a large number of subscribers use common equipment to communicate, when a user requests to start a communication, or requests to add a circuit in order to set up a higher-speed circuit, a circuit is allocated out of idle communication equipment resources, so that when the communication is completed, the allocated circuit is released so as to prepare for allocating the circuit for other communications.
Moreover, when allocating a circuit, whether there are idle (not in use) resources sufficient to fulfill a request for communication is determined so that, when there are sufficient resources, the call for communication is accepted, while otherwise the call requesting communication as described above is rejected, and a control method which maintains the quality of an already ongoing communication, or a call-admission control method, is performed.
In the meantime, services provided by such a communications system as described above include voice calls, video telephone, facsimile communication, file downloading, file transfer and the like, which are available to users of fixed telephones, portable telephones and the like. The users enter into correspondingly different contracts, such as fixed charging and variable charging, with operators who provide the services as described above.
Moreover, calls handled within a communications system include normal calls as well as emergency calls such as “110” (for the police), “119” (for the fire and ambulance) and the like. Within the communications system, these different kinds of calls exist simultaneously in large numbers so that shared resources are utilized. Since these shared resources are finite, in a case that the shared resources are allocated in the order of occurrence of the calls, when an emergency call such as “110” and the like occurs, the admission request of the emergency call ends up getting rejected in a case that no idle shared resources exist. In other words, in order to respond to various requests for communications from the users, it is necessary to efficiently allocate the resources to calls of different kinds.
Therefore, a method of call-admission control which, depending upon the importance or the priority of a call, differentiates the ease of allocation of the call is being proposed (for example, refer to Patent Document 1). According to this method of call-admission control, different threshold values are set for services of different priorities so that shared resources are allocated depending upon the priorities. A description is disclosed in which, thereby, call admission is controlled depending upon a service utilized by the user, avoiding degradation in communications quality.
Moreover, when many high-priority calls requesting a large amount of resources occur, even in a case where there are idle shared resources sufficient to be allocated to a low priority call requesting a small amount of resources, all of those call admission requests end up getting rejected until a release of a currently ongoing call occurs. Thus, in order to avoid this sort of problem, a method of call-admission control is considered such that, when there are not many idle shared resources, a call with a large amount of requested resources is rejected, while a call with a small amount of requested resources is admitted. A technology disclosed as described in Patent Document 2, the technology proposed from these viewpoints, by providing individual call-admission threshold values depending upon the required resource amount per type of call, even in a case that many communications requests requiring a large amount of resources exist, enables maintaining a high resource usage rate.
Patent Document 1
JP 2002-223239A
Patent Document 2
JP 2002-190830A
However, with the related-art method of call-admission control, there is a problem that, while the ease of allocation is differentiated depending upon the importance or the priority of a call, when there are no longer many idle shared resources, the resources cannot utilized efficiently.
Furthermore, when there are not many idle shared resources, a method of changing the ease of allocation of the shared resources depending on the required resource amount per type of call is adopted, whereas once there are no longer many idle shared resources, a call with a high resource requirement ends up getting rejected. Thus, there is a problem of not being able to differentiate the importance or the priority of calls.